Maybe "brush marks" wasn't the best way to describe it. If you have incomplete coverage in an area the light will show through in spots that are the thinnest.

I solved that by alternating horizontal and vertical coats. Latex is nice as clean up is with water. Also less worry about taping as there is no over spay to contend with. Latex will come off very easily from scratches but not from a little splashed/dripped water.